[0001] The present invention relates to a polymer composition with flame retardant properties,
to an electrical wire or cable coated with the polymer composition, and to an article
comprising the polymer composition.
[0002] Flame retardant behavior is crucial for various applications, especially in wire
and cable industry. The fire behavior of a material includes ease of thermal degradation,
ease of ignition, flame spread, rate of heat release, and ease of extinction which
may be complicated by smoke generation, toxic potency and other properties. A higher
rate of heat release causes fast ignition and flame spread. Furthermore, the rate
of heat release controls the fire intensity and is therefore much more important than
ignitability, smoke toxicity or flame spread. Typically, when flame retardants are
used to address these fire risks, they are specifically tailored to meet a respective
fire risk scenario.
[0003] Halogen containing polymer, such as polyvinyl chloride, is considered as a self-extinguishing
material due to its chemical composition with halogen atoms. However, when plasticizers
are added to soften the material, the flame retardant ability is significantly reduced
and the flame retardant additives are required to provide slow flame propagation.
Especially flame retardancy of polymer compositions containing a chlorine containing
polymer is crucial due to the toxic gases which may be otherwise released upon ignition.
In the art, typically antimony trioxide may be used working synergistically with halogen-containing
material, such as PVC. However, in commercial products only a small loading of antimony
trioxide is added due to its high price. Therefore, other mineral flame retardant
such as metal oxide is usually required at high loading to achieve good flame retardancy.
Such high filler/additive loading deteriorates mechanical properties, i.e. tensile
strength and elongation at break. Besides flame retardancy of a polymer composition
containing a flame retardant, also color stability of the polymer composition, after
extrusion, is an essential requirement.
[0004] The flame retardants of the art, such as magnesium dihydroxide (MDH) or aluminium
trihydrate (ATH), have the further disadvantages in that these hydrophilic compounds
are less incompatible with polymers, and require extra additives to get compounded
with the polymers. Typically, high loads are always required to get necessary flame
retardancy performance which can affect the mechanical properties of the composites,
and show a poor dispersion in the polymer. In addition, the flame retardants are chemically
non-flexible, only perform endothermic reaction to generate water.
[0005] More recently, the use of hydrotalcites or layered double hydroxides (LDHs) in the
synthesis of inorganic/organic nanocomposites has become a new emerging class of material.
[0007] Owing to the relatively high surface charge and hydrophilic properties of LDHs, the
particles or crystallites of conventionally synthesised LDHs are generally highly
aggregated. The result of this is that, when produced, LDHs aggregate to form "stone-like",
non-porous bodies with large particle sizes of up to several hundred microns and low
specific surface area of generally 5 to 15 m
2/g (as disclosed for example in
Wang et al Catal. Today 2011, 164, 198). These make LDHs not only be difficult to form LDH polymer composite but also have
poor dispersion in polymer which would lead to poor mechanical properties.
[0008] There have been attempts to modify LDHs to enable stable dispersions or good composites
to be formed.
WO 2009/080597A2 discloses a process for preparing an organically modified layered double hydroxide
with a reduced alkalinity and agglomerate formation.
WO 2007/065861 A relates to LDHs having fatty acid anions intercalated therein to promote compatibility
with polymers. But these organo-modified LDH materials often decompose at a relative
low temperature and require appropriate and expensive treatment of the LDH prior to
their incorporation into polymer matrix.
WO 2013/117957 A2 discloses the use of LDHs as flame retardants in a LDH polymer composite through
solvent mixing method for reduced flammability and smoke index. However, the solvent
mixing method is not practically in the industry.
[0009] It is an object of the present invention to provide a polymer composition having
improved flame retardancy, although miner amounts of flame retardant are added, as
well as preferably an improved color stability over time, especially through melt
mixing process.
[0010] This object is achieved by a polymer composition comprising 100 parts by weight of
halogen containing polymer, 10 to 70 parts by weight of plasticizer, 2 to 10 parts
by weight of stabilizer, 1 - 15 parts by weight of a layered double hydroxide (LDH)
having the formula
[M
z+1-xM'
y+x(OH)
2]
a+(X
n-)
a/
n·
bH
2O·
c(solvent) (I)
wherein M and M' are different and each is at least one metal cation,
z = 1 or 2;
y = 3 or 4, 0 <
x<0.9,
b = 0 to 10, c = 0 to 10, X is an anion,
n is the charge on the anion, and
a =
z(1-x)+
xy-2; solvent is organic solvent with a hydrogen bond donor or acceptor function.
[0011] In one embodiment, in formula (I), when z is 2, M is Mg, Zn, Fe, Ca, Sn, Ni or a
mixture of two or more of these, or, when z is 1, M is Li.
[0012] In a further embodiment, in formula (I), when y is 3, M' is Al, Ga, Y, In, Fe, Ti,
or a mixture thereof, or when y is 4, M' is Sn, Ti or Zr or a mixture thereof.
[0013] In one embodiment, the LDH has the formula
[(Mg
pZn
qSn
(II)r)
1-x(Al
sSn
(IV)t)
x(OH)
2]
a+(X
n-)
a/n•
bH
2O•
c(solvent)
wherein
p+
q+
r=1,
p = 0 - 1,
q = 0 - 1,
r = 0 - 1,
s+t = 1,
s = 0 - 1,
t = 0 - 1,
x = 0.10 - 0.40,
b = 0 to 10, c = 0 to 1 , X is an anion,
n is the charge on the anion, and
a = [(2
p+2
q+2
r)(1-
x)] + [(3s+4t)x] - 2 ; solvent is organic solvent with a hydrogen bond donor or acceptor
function.
[0014] In another embodiment, the LDH has the formula
[(Mg
pZn
q)
1-xAl
x(OH)
2]
a+(X
n-)
a/n·
bH
2O·
c(solvent)
wherein p+q = 1,
p = 0 - 1,
q = 0 - 1, x = 0.10 - 0.40,
b = 0 to 10, c = 0 to 1, X is an inorganic oxyanion,
n is the charge on the anion, and
a = [(2
p+2
q)(1-
x)]+3
x-2; solvent is ethanol.
[0015] In one embodiment, in LDH formula, x is preferably 0.10 - 0.33, more preferably 0.25
- 0.33;
b is preferably 0.1 -1, more preferably 0.1- 0.6; c is preferably 0 - 0.01, more preferably
0 - 0.0001, most preferably 0 - 0.000005;
p is preferably 0 - 0.67, more preferably 0 - 0.33;
q is preferably 0.33 -1, more preferably 0.67 - 1;
r is preferably 0.33 -1, more preferably 0.67 -
1; s is preferably 0.33 - 1, more preferably 0.7 - 1;
t is preferably 0 - 0.67, more preferably 0 - 0.3.
[0016] In another embodiment, the amount of solvent in LDH is in a range of 0-5,000 mg/kg
of total mass of LDH, preferably 0-50 mg/kg of total mass of LDH, more preferably
0-10 mg/kg of total mass of LDH.
[0017] In another embodiment, X is an anion selected from at least one of halide, inorganic
oxyanion, anionic surfactants, anionic chromophores and anionic UV absorbers, wherein
the inorganic oxyanion is preferably carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate,
nitrite, borate, nitrate, sulphate, phosphate or a mixture of two or more thereof.
[0018] The anion in the LDH may be otherwise any appropriate anion, organic or inorganic,
for example halide (e.g., chloride, bromide), inorganic oxyanions (e.g. X
mO
n(OH)
p-q; m = 1-5; n = 2-10; p = 0-4, q = 1-5; X = B, C, N, S, P: e.g. carbonate, bicarbonate,
hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate),
anionic surfactants (such as sodium dodecyl sulfate, fatty acid salts or sodium stearate),
anionic chromophores, and/or anionic UV absorbers, for example 4-hydroxy-3-10 methoxybenzoic
acid, 2-hydroxy-4 methoxybenzophenone-5-sulfonic acid (HMBA), 4-hydroxy- 3-methoxy-cinnamic
acid, p-aminobenzoic acid and/or urocanic acid.
[0019] The organic solvent with a hydrogen bond donor or acceptor function is, in any amount,
miscible with water. Hydrogen bond donor groups may include R-OH, R-NH
2, R
2NH, whereas hydrogen bond acceptor groups may include ROR, R
2C=O, RNO
2, R
2NO, R
3N, ROH, RCF
3 [R is hydrocarbyl group]. Exemplary organic solvents include ethyl acetate, acetone,
acetonitrile, dimethylformamide, dimethylsulfoxide, dioxane, ethanol, m-cresol, o-cresol,
p-cresol, methanol, n-propanol, isopropanol, n-butanol, sec-butanol, n-pentanol, n-hexanol,
eyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl
ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, butyl carbitol
acetate, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK),
methyl isoamyl ketone, methyl n-amyl ketone, isophorone, isobutyraldehyde, furfural,
methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate,
n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl
acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, n-butyl propionate, n-pentyl
propionate, triethylamine, 2-nitropropane, aniline, N,N-dimethylaniline, nitromethane,
tetrahydrofurane, and mixtures of two or more thereof. Preferably, the solvent is
ethanol or acetone.
[0020] In one embodiment, the LDH has a volatile content which is presented as
b +
c in the range of 0 - 1, preferably 0 - 0.6. The volatile content refers to the amount
of volatile substance where the volatile substance are water, solvent or a mixture
thereof. The volatile content is measured by Karl fisher titration technique for water
content and gas chromatography/mass spectrometry GC/MS headspace technique for solvent
content.
[0021] Halogen containing polymers are homopolymers or copolymers containing halogen, preferably,
chlorine containing polymer. Chlorine containing polymer includes polyvinyl chloride,
polyvinylidene chloride, ethylene-vinyl chloride copolymer, vinyl chloride-propylene
copolymer, chlorinated polyethylene, chlorinated polypropylene, chlorinated butyl
rubber, chlorosulfonated polyethylenes, and the like. In a more preferred embodiment,
the chlorine containing polymer is polyvinyl chloride.
[0022] In one embodiment, the LDH is present in the polymer composition in the range of
3 to 10 parts by weight per 100 parts by weight of the halogen containing polymer.
[0023] In a further embodiment, a particle size distribution of the LDH is in the range
of 0.05 - 5 µm, preferably in the range of 0.1 to 3 µm. The particle size distribution
is measured by laser diffraction particle size analysis technique.
[0024] In a further embodiment, the LDH has a specific surface area in the range of 50 to
500 m
2/g, preferable in the range of 80 to 100 m
2/g. The specific surface area is measured by Brunauer Emmett-Teller (BET) analysis
technique.
[0025] In another embodiment, the plasticizer comprises at least one plasticizer selected
from the group of phthalate, mellitate, adipate, azelate, maleate, sebacate, epoxidized
oil, chlorinated paraffin oil, polymeric plasticizer or a mixture thereof. Preferably,
the mixtures of phthalate and mellitate. Exemplary plasticizers include bis(2-ethylhexyl)
phthalate (DEHP), bis(2-propylheptyl) phthalate (DPHP), diisononyl phthalate (DINP),
di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBzP), diisodecyl phthalate (DIDP),
dioctyl phthalate (DOP), diisooctyl phthalate (DIOP), diethyl phthalate (DEP), diisobutyl
phthalate (DIBP), di-n-hexyl phthalate, trimethyl trimellitate (TMTM), tri-(2-ethylhexyl)
trimellitate (TEHTM), tri-(n-octyl,n-decyl) trimellitate, tri-(heptyl,nonyl) trimellitate,
n-octyl trimellitate (OTM), bis(2-ethylhexyl)adipate (DEHA), dimethyl adipate (DMAD),
Monomethyl adipate (MMAD), dioctyl adipate (DOA), dibutyl sebacate (DBS), dibutyl
maleate (DBM), diisobutyl maleate (DIBM), polyester plasticizer, and mixtures of two
or more thereof.
[0026] In a further embodiment, the stabilizer comprises at least one stabilizer selected
from the group of lead-based stabilizer, mixed metal-based stabilizer or a mixture
thereof, preferably lead-based stabilizer. Exemplary lead-based stabilizer include
tetra-basic lead sulphate, tribasic lead sulphate, di-basic lead phosphite, di-basic
lead phthalate, di-basic lead stearate, normal lead stearate, calcium-zinc stabilizers,
barium-zinc stabilizers, calcium- barium-zinc stabilizers and mixtures of two or more
thereof.
[0027] The plasticizer included in the polymer composition is for increase of the plasticity
or for reducing the viscosity of the polymer composition. The plasticizer also lowers
the glass temperature of the polymer. Thus, the polymer is easier to process when
adding the plasticizer. In addition, the plasticizer may make rigid polymer to be
soft polymer, for example PVC, which is useful for making wire and cable sheaths.
[0028] The stabilizer is included in the polymer composition for stabilizing the polymer
composition during and after processing at high temperature and under high pressure.
Without a stabilizer, the polymer will easily degrade/discolor.
[0029] In further embodiment, the LDH may comprise a surface-treating agent to then result
in a layered double-hydroxide with the formula as below:
[M
z+1-xM'
y+x(OH)
2]
a+(X
n-)
a/n·bH
2O·
c(solvent) ·
d(surface-treating agent)
wherein M and M' are different and each is at least one metal cation,
z = 1 or 2;
y = 3 or 4, 0 <x<0.9,
b = 0 to 10,
c = 0 to 10,0 <
d ≤ 10, X is an anion, n is the charge on the anion, and
a =
z(1-x)
+xy-2; solvent is organic solvent with a hydrogen bond donor or acceptor function.
[0030] The surface-treating agent is an organic moiety capable of covalent or ionic association
with at least one surface of the layered double hydroxide, and which modifies the
surface properties of the layered double hydroxide. It will be appreciated that the
at least one surface of the LDH may be external or internal (i.e. the surface-treating
agent may be intercalated between the cationic layers). The surface-treating agent
may be ionically associated with the surface of the LDH via a polar or charged group
located on the surface-treating agent. Alternatively, the surface-treating agent may
be covalently bonded to the surface of the LDH, for example to one or more hydroxyl
groups located on the LDH's surface. Suitably, the surface-treating agent is covalently
or ionically associated with at least one surface of the layered double hydroxide.
In an embodiment, the surface-treating agent is an organic moiety comprising at least
4 carbon atoms and at least one functional group that is capable of covalent or ionic
association with at least one surface of the layered double hydroxide. In another
embodiment, the surface-treating agent is an organosilane compound, a surfactant or
a mixture thereof. Alternatively, the surface-treating agent may be citric acid, or
a salt thereof (e.g. sodium citrate). The organosilane compound may be a hydroxysilane,
an alkoxysilane, siloxane, or polysiloxanes (e.g. polydimethylsiloxane). In an embodiment,
the organosilane compound is selected from the group consisting of 3-aminopropyltriethoxysilane,
(3-glycidyloxypropyl)triethoxysilane (3-mercaptopropyl)triethoxysilane, triethoxyvinylsilane,
triethoxyphenylsilane, trimethoxy(octadecyl)silane, vinyl-tris(2-methoxy-ethoxy)silane,
g-methacryloxypropyltrimethoxysilane, g-aminopropyltrimethoxysilane, b(3,4-epxycryclohexyl)ethyltrimethoxysilane,
g-glycidoxypropyltrimethoxysilane, g-mercaptopropyltrimethoxysilane, (3-aminopropyl)triethoxysilane,
N-(3-triethoxysilylpropyl)ethylenediamine, 3-aminopropyl-methyl-diethoxysilane, vinyltrimethoxysilane,
chlorotrimethylsilane, tert-butyldimethylsilyl chloride, trichlorovinylsilane, methyltrichlorosilane,
3-chloropropyl trimethoxysilane, chloromethyltrimethylsilane, diethoxydimethyl silane,
propyltrimethoxysilane and γ-piperazinylpropylmethyldimethoxysilane. Suitably, the
organosilane compound is selected from the group consisting of 3-aminopropyltriethoxysilane,
(3-glycidyloxypropyl)triethoxysilane (3-mercaptopropyl)triethoxysilane. Triethoxyvinylsilane,
trimethoxymethylsilane and triethoxyphenylsilane. When used herein in relation to
the surface-treating agent, it will be understood that the term surfactant means any
compound having a hydrophilic portion capable of ionic or covalent association with
the surface of the LDH, and a lipophilic portion. In an embodiment, the surfactant
is a cationic, anionic, non-ionic or amphoteric surfactant. Exemplary surfactants
include sodium dodecyl sulphate and sodium dodecylbenzenesulfonate. In another embodiment,
the surfactant is a fatty acid, preferably having 4-22 carbon atoms, or a salt thereof,
a fatty acid/phosphoric acid ester, or polyhydric alcohol esters. Exemplary surfactants
include butyric acid, caproic acid, lauric acid, myristic acid, palmitic acid, stearic
acid, hydroxystearic acid, arachidic acid, oleic acid, linoleic acid, maleic acid,
or a salt thereof. Suitably, the surfactant is selected from stearic acid, lauric
acid, or a salt thereof (e.g. sodium salts, magnesium salts, calcium salts, zinc salts).
Preferably, LDH is surface-treated with calcium stearate or zinc stearate. The surface
treating agents attach to the surface of LDH for preventing moisture and/or volatile
substance to absorb into the LDH structure and/or on the LDH surface during storage
time.
[0031] In one embodiment, d has a value according to the expression 0.01
< d ≤ 5. Suitably,
d has a value according to the expression 0.01 <
d ≤ 3.
d may also have a value according to the expression 0.1 <
d ≤ 3 or 1 < d ≤ 3.
[0032] In further embodiment, the polymer composition may comprise a lubricant, a processing
aid, a further flame retardant agent other than the LDH, a filler, a pigment (e.g.
iron oxide pigment, carbon black), an antioxidant or a mixture thereof.
[0033] Lubricant may be selected from acid amides (e.g. erucamide, oleamide, stearamide),
acid esters (e.g. stearyl stearate, distearyl phthalate), fatty acids (e.g. lauric,
myristic, palmitic, stearic), oleic, erucic), hydrocarbon waxes (e.g. polyethylene,
polypropylene, paraffin), metallic soaps (e.g, calcium stearate, zinc stearate, magnesium
stearate) or the mixtures thereof.
[0034] Processing aid may be selected from acrylic-based processing aids, fluoropolymers,
silicone process aid or the mixtures thereof.
[0035] Flame retardant agent may be selected from organic phosphorus compounds (e.g. phosphates,
phosphonates), halogenated flame retardant (e.g. brominated flame retardant), antimony
trioxide, silicon dioxide, organically cationic clay, hydrated minerals such as hydroxides,
hydrated oxides, or hydrated salts of metals (e.g. alumina trihydrate (ATH), magnesium
dihydroxide (MDH)), or the mixtures thereof.
[0036] Filler may be selected from calcium carbonate, silica,barites, talc, mica, magnesium
carbonate or silica.
[0037] In one embodiment, the polymer composition comprises PVC 100 parts by weight, plasticizer
10 - 70 parts by weight, stabilizer 3 - 7 parts by weight, lubricant 0.1 - 1 parts
by weight, filler 0 - 80 parts by weight, processing aid 0 - 3 parts by weight, the
LDH 3 - 10 parts by weight, pigment 0 - 2 parts by weight and other flame retardant
0 -10 parts by weight.
[0038] In one embodiment, the polymer composition comprises PVC 100 parts by weight, phthalate
plasticizer 10 - 35 parts by weight, mellitate plasticizer 5 - 30 parts by weight,
lead-based stabilizer 3 - 7 parts by weight, oxidized PE wax 0.1 - 1 parts by weight,
calcium carbonate 20 - 70 parts by weight, acrylic processing aid 0 - 3 parts by weight,
the LDH 3 -10 parts by weight, pigment 0 - 2 parts by weight and other flame retardant
0 - 10 parts by weight.
[0039] In one embodiment, the polymer composition is compounded by melt mixing process at
high temperature, preferably 150 - 190°C, more preferably 160-180°C and processing
speed in the range of 30 -100 rpm, preferably 40 -60 rpm. The melt mixing process,
for example, is single screw extrusion process, twin screw extrusion process or injection
process.
[0040] According to the invention is also an article comprising the inventive polymer composition,
wherein the article is an electric or electronic circuit component, a structural element
for transportation and building or an indoor every day object.
[0041] Finally, according to the invention is also an electrical wire or cable coated with
the polymer composition according to the invention.
[0042] It was surprisingly found that the polymer composition of the present invention provides
excellent flame retardant properties as well as improved color stability and mechanical
properties. Additionally, the polymer composition may be provided with superior flame
retardancy properties although the flame retardant is added in low amounts. It was
also surprisingly found that, in one embodiment, the color stability is better the
higher Zn or Sn content in the LDH is. The polymer composition of the present invention
also has a good, stable and transparent dispersion of LDH in polymer, reduction of
plate-out formation (die buildup) in extrusion process, reduction of void or pinhole,
and improvement of processability.
[0043] LDHs used in the polymer composition of the present invention may be [(Mg
0.33Zn
0.66)
0.75Al
0.25(OH)
2][CO
3]
0.125·
bH
2O·
c(solvent), [Zn
0.67Al
0.33(OH)
2][B
4O
7]
0.17•
bH
2O•
c(solvent) or [Mg
0.75(Al
0.7Sn
0.3)
0.25(OH)
2][CO
3]
0.16•
bH
2O•
c(solvent). Especially these compounds show best results regarding color stability,
require only low dosage to be active as a flame retardant, show better flame retardancy
performance and higher thermal stability, compared to flame retardants of the art.
[0044] The LDH can be prepared based on methods as known in the art. For example, a method
is disclosed in
WO 2015/144778 A1 and comprises the steps:
- a) precipitating a layered double hydroxide having the formula
[Mz+1-xM'y+x(OH)2]a+(Xn-)a/n•bH2O wherein M, M', z, y, x, a, b and X are as defined above for formula (I) from a solution containing the cations
of the metals M and M' and the anion Xn-;
- b) ageing the layered double hydroxide precipitate obtained in step a) in the original
solution;
- c) collecting, then washing the layered double hydroxide precipitate;
- d) dispersing the wet layered double hydroxide in a solvent so as to produce a slurry
of the layered double hydroxide in the solvent;
- e) maintaining the dispersion obtained in step d);
- f) optionally, dispersing in surface-treating agent;
- g) optionally, maintaining the dispersion obtained in step f)
- h) recovering and drying the layered double hydroxide ; and
- i) optionally, thermal treating the layered double hydroxide obtained in step h)
[0045] In step a) of the above method, the layered double hydroxide will typically be produced
by adding an aqueous precursor solution containing ions of the metals M and M' into
a solution containing the anion X which may additionally contain NaOH or to which
NaOH solution may be added separately in order to adjust the pH of the solution to
a predetermined value, typically greater than 7, preferably greater than 8, more preferably
9-10. It is, according to a preferred embodiment, desirable to add the metal precursor
solution to the anion solution rapidly with vigorous stirring since this promotes
rapid nucleation of the LDH. In one embodiment, a loading rate of the aqueous precursor
into a solution containing the anion X is greater than 1,200 ml/minute, preferably
greater than 1,400 ml/minute, more preferably in the range of 1,400 - 1,600 ml/min.
In another embodiment, a speed for stirring is greater than 300 rpm, preferably greater
than 400 rpm, more preferably 500 - 800 rpm. We have found that this rapid addition
and quick co-precipitation stage causes the LDH colloid formed to have a smaller and
thinner particle size. The LDH is subjected to ageing in the original reaction solution
and, preferably, the solution containing the precipitated LDH will be aged for less
than 12 hours, preferably 1 - 5 hours and more preferably 3 - 4 hours. In step c)
of the method, the precipitated layered double hydroxide is collected and then washed.
Typically, the precipitate is collected by filtration, preferably vacuum filtration.
After collection, the precipitate is washed until the washing solution has a pH which
is substantially neutral, for example pH 7 ± 0.5. Washing is typically carried out
using deionised water.
[0046] According to the above method, the collected and washed LDH is re-dispersed in the
solvent so as to produce a slurry of the LDH in the solvent. Preferably, solvent is
ethanol.
[0047] The dispersion of LDH in the solvent is maintained preferably in the range of 30
minutes to 2 hours, preferably 1 to 2 hours, it is preferred that the dispersion is
maintained under agitation and/or stirring. Stirring can be carried out using an overhead
mixer at a stirring speed which is preferably at least 300 rpm and more preferably
500 - 800 rpm.
[0048] In further embodiment, the step f) may be conducted by a variety of means. In its
simplest form, step f) comprises mixing the LDH provided in step e) with the surface-treating
agent. In another embodiment, the LDH provided in step e) is calcined before mixing
with the surface-treating agent in step f).
[0049] According to one preferred embodiment, the step h) of recovering and drying the LDH
comprises filtering the LDH from the organic solvent and then subjecting the collected
LDH to drying. Drying may be carried out in an oven, with or without applied vacuum
for 8 - 16 hours. Typically, oven drying will be carried out at a relatively low temperature
which will be dependent on the temperature at which the organic solvent evaporates.
Preferably, the drying step, when the solvent is ethanol, will be carried out at a
temperature in the range of room temperature (20°C) to 70°C. In the preferred embodiment
according to which ethanol is used as the organic solvent, we have found that an oven
temperature of about 65°C for overnight may be used to dry the collected LDH.
[0050] According to a different preferred embodiment, the step h) of the method comprises
passing the dispersion of LDH in the organic solvent to a spray drying apparatus and
then spray drying the dispersion, typically using an inert atmosphere such as nitrogen,
so as to produce a spray dried LDH.
[0051] According to one preferred embodiment, the step i) of thermal treating the LDH comprises
heating the LDH to evaporate solvent and water. The thermally treated LDH may have
the amount of solvent in a range of 0-5,000 mg/kg of total mass of LDH, preferably
0-50 mg/kg of total mass of LDH, more preferably 0-10 mg/kg of total mass of LDH.
Thermal treating may be carried out in an oven, vacuum oven, and/or disc dryer. Preferably,
the thermal treating step, when the solvent is ethanol, will be carried out at a temperature
100°C to 110°C.
[0052] Further features and advantages of the present invention will now be illustrated
in the following detailed description by means of examples and is further illustrated
by the drawings.
[0053] In the drawing,
Fig. 1 illustrates the tensile strength before aging of polymer compositions prepared
according to Example 2;
Fig. 2 illustrates the elongation at break before aging of polymer compositions prepared
according to Example 2;
Fig. 3 illustrates the retention of tensile strength after heat aging of polymer compositions
prepared according to Example 2;
Fig. 4 illustrates the elongation at break after heat aging for polymer compositions
prepared according to Example 2;
Fig. 5 illustrates the retention of tensile strength after oil aging of polymer compositions
prepared according to Example 2;
Fig. 6 illustrates the retention of elongation at break after oil aging for polymer
compositions prepared according to Example 2; and
Fig. 7 illustrates the smoke density of PVC compositions prepared according to Example
2.
[0054] The abbreviations used in the below examples and tables have the following meanings
LDH-CO3 |
: LDH having the formula (I) whereas the anion (Xn-) is carbonate |
LDH-B4O7 |
: LDH having the formula (I) whereas the anion (Xn-) is borate |
Mg3Al-CO3 |
: [(Mg0.75Al0.25(OH)2][CO3]0.5•nH2O; common Hydrotalcite without solvent treatment |
Mg2.5Zn0.5Al-CO3 |
: [(Mg0.83Zn0.17) 0.75Al0.25(OH)2][CO3]0.125•bH2O•c(solvent) |
Mg2ZnAl-CO3 |
: [(Mg0.66Zn0.33)0.75Al0.25(OH)2][CO3]0.125•bH2O•c(solvent) |
Mg1.5Zn1.5Al-CO3 |
: [(Mg0.5Zn0.5)0.75Al0.25(OH)2][CO3]0.125•bH2O•c(solvent) |
MgZn2Al-CO3 |
: [(Mg0.33Zn0.66)0.75Al0.25(OH)2][CO3]0.125•bH2O•c(solvent) |
Mg3Al0.7Sn0.3-CO3 |
: [(Mg)0.75(Al0.7Sn0.3)0.25(OH)2][CO3]0.16•bH2O•c(solvent) |
Zn2Al- B4O7 |
: [(Zn)0.67(Al)0.33(OH)2][B4O7]0.17•bH2O•c(solvent) |
ATH |
: Aluminium trihydrate |
Synthesis of LDHs of the invention
Synthesis of LDH-CO3 (LDH-C 1 to 5)
[0055] LDH-C 1 to 5 were synthesized by adding a metal precursor solution drop-wise into
1.4L of a 1.5 M Na
2CO
3 solution with a drop rate of 36 ml/minute. The pH of the precipitation solution was
controlled at 10 using a NaOH solution (12M). After 4 hours of ageing in original
solution, the resulting slurry was filtered by vacuum filtration technique and washed
with deionized water until a pH is 7 was obtained. The filtered slurry was washed
with ethanol for 1 hour, and then was dried by vacuum oven at 65°C overnight. The
metal precursor solution were prepared by dissolving metals as stated in Table 1 in
1.4 L water.
Table 1
|
LDH-C1 Mg2.5Zn0.5Al-CO3 |
LDH-C2 Mg2ZnAl-CO3 |
LDH-C3 Mg1.5Zn1.5Al-CO3 |
LDH-C4 MgZn2Al-CO3 |
LDH-C5 Mg3Al0.7Sn0.3-CO3 |
Metal precursor solution |
Zn(NO3)2·6H2O (kg) |
0.094 |
0.189 |
0,283 |
0.379 |
- |
Mg(NO3)2·6H2O (kg) |
0.407 |
0.326 |
0.244 |
0.163 |
0.490 |
Al(NO3)3·9H2O (kg) |
0.239 |
0.239 |
0.239 |
0.239 |
0.168 |
SnCl4·5H2O (kg) |
- |
- |
|
- |
0.050 |
Synthesis of Zn2Al-B4O7 (LDH-B 1)
[0056] LDH-B 1 was synthesized by adding a metal precursor solution drop-wise into a 1.4L
of 1.5 M Na
2 B
4O
7 solution with a drop rate of 36 ml/ minute. The pH of the precipitation solution
was controlled at 9 using a NaOH solution (12M). After 4 hours of ageing in original
solution, the resulting slurry was filtered by vacuum filtration technique and washed
with deionized water until a pH is 7 was obtained. The filtered slurry was washed
with ethanol for 1 hour, and then was dried by vacuum oven at 65°C overnight. The
metal precursor solution was prepared by mixing 379.3 g of Zn(NO
3)
2·6H
2O, 239.1 g of Al(NO
3)
3·9H
2O in 1.4L of water.
Characterisation methods
[0057]
- a) Color stability of prepared LDHs filled PVC compositions was evaluated after extrusion
by eyes and by spectrophotometer CM-3600A (Konica Minolta). LDH filled PVC compositions
were compression molded into 11 x 11 cm2 square plaques of uniform thickness (approximately 3 mm.) for measurement whiteness
index (WI),yellowness index (YI), L*, a*, b*, C, h and delta E by spectrophotometer.
- b) Determination of physical properties of the polymer composites
- 1. Tensile strength and %Elongation is measured by IEC60502. The specimen in dumbbell shape is extended at the cross
head speed of 200 mm/min by using the test machine U.T.M. The breaking point is measured.
Tensile strength and elongation are calculated by the following formula.
- 2. Tensile strength and %Elongation after heat aging is measured by IEC60502. The specimen in dumbbell shape is heated at 100°C for 168
hours before extended at the cross head speed of 200 mm/min by using the test machine
U.T.M. The breaking point is measured. Retention of tensile strength and elongation
at break are calculated by the following formula.
- 3. Tensile strength and %Elongation after oil aging is measured by IRM902. The specimen in dumbbell shape is heated in oil at 70°C for
4 hours before extended at the cross head speed of 200 mm/min by using the test machine
U.T.M. The break-ing point is measured. Retention of tensile strength and elongation
at break are calculated by the formula as shown in 2.
- c) Flame-retardant performance of prepared LDHs filled PVC compositions was evaluated
using a cone calorimetry (Toyoseiki). Approximately 30 g of PVC composition was compression
molded into 10 cm X 10 cm square plaques of uniform thickness (approximately 3 mm.)
before the tests were performed. A cone-shape heater with incident flux of 50 kW/m2
was used, and the spark was continuous until the sample ignited. The results from
cone calorimeter are generally considered to be reproducible to +/- 10%. This provides
the peak heat release rate (PHRR) and ignition time. The fire performance index (FPI)
which is the ratio between the ignition time and the peak rate of heat release.
- d) Congo red test of prepared LDH filled PVC compositions was evaluated by putting
1-g sample into the test tube which will be placed in the heating block at 180°C.
Litmus paper will be placed at the top of the tube. Once the paper turns red, the
time is recorded indicating the emission of acid gas from the composition.
- e) Smoke density test is measured by ASTM E 662. Sample was prepared into 3 x 3 inches
with 3 mm thickness. The test was performed with non-flaming mode where the sample
was radiated with heat source (2.5 W/cm2). As smoke generated, optical transmission was measured. The specific optical density
(Ds) is then calculated and plotted against time.
Example 1
[0058] PVC compositions, Comparative example 1-7 (Com.Ex.1-7) and Embodiment 1-14 (Em. 1-14),
were prepared by dry blending 100 parts by weight of PVC resin, 4 parts by weight
of tribasic lead sulphate, 20 parts by weight of 1,2-benzenedicarboxylic acid diisodecyl
ester, 10 parts by weight of tris(2-ethylhexyl) trimellitate, 5 parts by weight of
chlorinated paraffin oil, 5 parts by weight of epoxidized soybean oil, 50 parts by
weight of CaCO
3, 0.2 parts by weight of epoxidized PE wax, 3 parts by weight of antimony trioxide,
2 parts by weight of silicon dioxide,1 parts by weight of acrylic processing aid,
and the prepared LDH-CO
3, the prepared LDH- B
4O
7, common hydrotalcite (Mg
3Al-CO
3) or ATH in an amount as dictated in table 2 and 3in high speed mixer at 500 - 2,000
rpm and heat up to 120°C to produce a uniform powder mixture. Then, melt mixing the
dry blend by single screw extruder at a temperature of 160-180 °C with a screw speed
of 60 rpm to form LDHs filled PVC pellet. The prepared composition have been tested
and analyzed, the results are given in Table 2 and 3 below.
Table 2: Color stability of polymer composition prepared with LDHs having various
metal types
|
Com. Ex 1 |
Com. Ex 2 |
Em. 1 |
Em. 2 |
Em. 3 |
Em. 4 |
Em. 5 |
Em. 6 |
LDHs (parts by weight) |
LDH-C1 |
- |
- |
30 |
|
|
|
|
|
LDH-C2 |
- |
- |
|
30 |
|
|
|
|
LDH-C3 |
- |
- |
|
|
30 |
|
|
|
LDH-C4 |
- |
- |
|
|
|
30 |
|
|
LDH-C5 |
- |
- |
|
|
|
|
30 |
|
LDH-B1 |
- |
- |
|
|
|
|
|
30 |
Mg3Al-CO3 |
- |
30 |
|
|
|
|
|
|
Color stability |
Color by eye |
White |
Black |
Dark brown |
Brown |
Yellow |
Quite white |
Quite white |
Quite white |
WI |
40.73 |
-39.67 |
-129.1 |
-103.1 |
-27.28 |
43.84 |
-25.62 |
25.77 |
YI |
4.85 |
40.75 |
75.66 |
59.94 |
33.69 |
6.65 |
31.83 |
12.92 |
L* |
78.56 |
67.38 |
52.78 |
49.24 |
70.76 |
80.8 |
70.77 |
78.34 |
a* |
-0.85 |
9.37 |
14.34 |
9.75 |
5.97 |
0.72 |
4.82 |
1.42 |
b* |
2.51 |
13.15 |
22.08 |
16.47 |
12.15 |
2.76 |
11.82 |
5.28 |
c |
2.65 |
16.14 |
26.33 |
19.14 |
13.54 |
2.85 |
12.76 |
5.47 |
h |
108.64 |
54.51 |
57 |
59.36 |
63.85 |
75.27 |
67.79 |
74.91 |
dE |
- |
18.5 |
35.8 |
34.2 |
14.2 |
2.75 |
13.4 |
3.58 |
[0059] As table 2, for the inventive polymer compositions (Em.1-6), it was found in a preferred
embodiment that an increase of Zn-content in the LDH and an incorporation of Sn(IV)
in the LDH results in a less yellowing (browning) of the polymer/LDH composition after
processing at high temperatures and pressures while common hydrotalcite, Mg
3Al-CO
3(Com.Ex 2) provides a dark brown/black material after processing compared to the PVC
composition without LDHs (Com.Ex 1).
Table 3: Mechanical and flame retardancy properties of PVC composition
|
Com. Ex 3 |
Com. Ex 4 |
Com. Ex 5 |
Com. Ex 6 |
Com. Ex 7 |
Em. 7 |
Em. 8 |
Em. 9 |
Em. 10 |
Em. 11 |
Em. 12 |
Em. 13 |
Em. 14 |
Composition |
Type |
ATH |
Mg3Al-CO3 |
LDH-C4 |
LDH-B1 |
|
parts by weight |
30 |
3 |
5 |
7 |
10 |
3 |
5 |
7 |
10 |
3 |
5 |
7 |
10 |
Property |
Method |
Spec |
|
Specific gravity |
ASTM D 792 |
- |
1.568 |
1.516 |
1.523 |
1.528 |
1.547 |
1.527 |
1.531 |
1.536 |
1.548 |
1.518 |
1.518 |
1.513 |
1.516 |
Tensile strength, MPa |
IEC 60502 |
Min. 12.5 |
23.4 |
22.6 |
22.4 |
20.9 |
16.7 |
24.6 |
24.1 |
25.3 |
24.4 |
23.5 |
23.3 |
23.8 |
22.7 |
Elongation at break, % |
IEC 60502 |
Min. 150 |
277 |
288 |
279 |
245 |
114 |
261 |
268 |
305 |
302 |
271 |
261 |
266 |
249 |
After heat aging at 100°C, 168h |
Method |
Spec |
|
Tensile strength, MPa |
IEC 60502 |
Min. 12.5 |
21.7 |
21.8 |
21.3 |
19.7 |
20.1 |
22.6 |
22.3 |
22.6 |
22.9 |
22.8 |
22.3 |
22.7 |
21.6 |
Elongation at break, % |
IEC 60502 |
Min. 150 |
254 |
250 |
245 |
200 |
5 |
274 |
269 |
265 |
251 |
225 |
253 |
248 |
233 |
Retention of tensile strength, % |
IEC 60502 |
75-125 |
93 |
96.4 |
95.2 |
94.1 |
120.5 |
92 |
93 |
89 |
94 |
91.7 |
97.5 |
93.8 |
100.0 |
Retention of elongation at break, % |
IEC 60502 |
75-125 |
92 |
86.8 |
87.9 |
81.5 |
4.4 |
105 |
100 |
87 |
83 |
83.1 |
96.9 |
93.0 |
93.6 |
Flammability Behavior at 50 kW/m2 |
Method |
Spec |
|
Ignition time (sec) |
- |
- |
46.2 |
- |
- |
- |
- |
20.3 |
160.9 |
351.6 |
410.9 |
78.1 |
136.2 |
286.3 |
61.5 |
Peak heat release rate (kW/m2) |
- |
- |
160.23 |
- |
- |
- |
- |
127.67 |
118.39 |
104.31 |
95.50 |
138.49 |
130.30 |
113.54 |
22.24 |
Fire performance index, s.m2/kW |
- |
- |
0.47 |
0.23 |
0.17 |
0.16 |
0.21 |
0.16 |
1.36 |
3.37 |
3.58 |
0.56 |
1.05 |
2.52 |
6.71 |
Congo red (min) |
- |
min 120 |
503 |
- |
- |
- |
- |
450 |
373 |
355 |
380 |
375 |
350 |
340 |
305 |
[0060] As table 3, the use of the LDHs (Em. 7 to 14) prolongs ignition time and decreases
peak heat release rate (PHRR). The fire performance index (FPI) is a correlation to
time to flashover of a material under burning situation. Consequently, FPI can be
used to predict time available for escape. Therefore, the higher the index, the better
the material is in term of flame retardancy. For both LDH systems LDH-CO
3 (Em. 7 to 10), and LDH-B
4O
7 (Em.11 to 14), only 5 - 10 parts by weight additions are needed in order to get over
100% improvement in FPI compared with 30 parts by weight addition of ATH for existing
PVC formulations (Com. Ex 3). In addition, the common hydrotalcite (Com. Ex 4 to 7)
shows worse FPI, tensile strength and elongation at break compared to the LDHs at
the same amount of addition.
[0061] It was also found that the use of the LDH allows a reduction of the amount of the
LDH compared to the use of, for example, ATH in the composite to nevertheless provide
improved flame retardant properties. For example, better flame retardant properties
may be obtained for the LDH of the present invention using 5 or 7 or 10 parts by weight
compared to the use of 30 parts by weight of ATH.
[0062] In addition, it was also found that the use of the LDH lessen the Congo red value.
The Congo red test is used for evaluating the dehydrochlorination rate which is the
rate of HCl release from the heating of PVC composition pellet. The released HCl accelerates
the PVC degradation which eventually generates crosslinked material. This crosslinked
material can also act as barrier to retard flame spread. In PVC/LDH, the better flame
retarding performance can then be related to the lower the Congo Red value as faster
barrier formation to better protect flame spread. However, the lower the Congo Red
value does not affect to the processing because the Congo Red value is still longer
than the resident time of material during processing.
Example 2
[0063] PVC compositions, PVC/ATH and PVC/LDH, were prepared by dry blending 100 parts by
weight of PVC resin, 4 parts by weight of tribasic lead sulphate, 20 parts by weight
of 1,2-benzenedicarboxylic acid diisodecyl ester, 10 parts by weight of tris(2-ethylhexyl)
trimellitate, 5 parts by weight of chlorinated paraffin oil, 5 parts by weight of
epoxidized soybean oil, 50 parts by weight of CaCO3, 0.2 parts by weight of epoxidized
PE wax, 3 parts by weight of antimony trioxide, 2 parts by weight of silicon dioxide,
1 parts by weight of acrylic processing aid, 0.8 parts by weight of carbon black,
and 30 parts by weight of ATH or 7 parts by weight of the prepared MgZn
2Al-CO
3, in high speed mixer at 500 - 2,000 rpm and heat up to 120°C to produce a uniform
powder mixture. Then, melt mixing the dry blend by single screw extruder at a temperature
of 160-180 °C with a screw speed of 60 rpm to form LDHs filled PVC pellet. The prepared
composition have been tested and analyzed, the results are given in Figs. 1 to 7.
[0064] As Figs. 1 to 7, the addition of the LDHs reduces smoke generation as compared with
the ATH-filled PVC composition. In addition, the PVC/LDH shows better mechanical performance
than that of PVC/ATH system.
[0065] The features disclosed in the foregoing description and in the claims may, both separately
and in any combination be material for realizing the invention in diverse forms thereof.
1. A polymer composition comprising
100 parts by weight of halogen containing polymer,
10 to 70 parts by weight of plasticizer,
2 to 10 parts by weight of stabilizer,
1-15 parts by weight of a layered double hydroxide (LDH) having the formula
[Mz+1-xM'y+x(OH)2]a+(Xn-)a/n•bH2O•c(solvent) (I)
wherein M and M' are different and each is at least one metal cation, z = 1 or 2; y = 3 or 4, 0 <x<0.9, b = 0 to 10, c = 0 to 10, X is an anion, n is the charge on the anion, and a = z(1-x)+xy-2; solvent is organic solvent with a hydrogen bond donor or acceptor function.
2. The polymer composition according to claim 1, wherein, in formula (I), when z is 2,
M is Mg, Zn, Fe, Ca, Sn, Ni, or a mixture of two or more of these, or when z is 1, M is Li.
3. The polymer composition according to claim 1 or 2, wherein, in formula (I), when y is 3, M' is Al, Ga, Y, In, Fe, Ti, or a mixture thereof, or, when y is 4, M' is Sn, Ti or Zr or a mixture thereof.
4. The polymer composition according to any of the preceding claims, whereinthe LDH has
the formula
[(MgpZnqSn(II)r)1-x(AlsSn(IV)t)x(OH)2]a+(Xn-)a/n•bH2O•c(solvent)
wherein p+q+r = 1, p = 0 - 1, q = 0 - 1, r = 0 - 1, s+t = 1, s = 0 - 1, t = 0 -1, x = 0.10 - 0.40, b = 0 to 10, c = 0 to 1, X is an anion, n is the charge on the anion, and a = [(2p+2q+2r)(1-x)] + [(3s+4t)x] - 2 ; solvent is organic solvent with a hydrogen bond donor or acceptor function.
5. The polymer composition according to any of the preceding claims, wherein the LDH
has the formula
[(MgpZnq)1-xAlx(OH)2]a+(Xn-)a/n•bH2O•c(solvent)
wherein p+q = 1, p = 0-1, q = 0 - 1, x = 0.10 - 0.40, b = 0 to 10, c = 0 to 1, X is an inorganic oxyanion, n is the charge on the anion, and a = [(2p+2q)(1-x)]+3x-2; solvent is ethanol.
6. The polymer composition according to any of the preceding claims, wherein X is an
anion selected from at least one of halide, inorganic oxyanion, anionic surfactants,
anionic chromophores, and anionic UV absorbers, wherein the inorganic oxyanion is
preferably carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite,
borate, nitrate, sulphate, phosphate, or a mixture of two or more thereof.
7. The polymer composition according to any of the preceding claims, wherein the organic
solvent with a hydrogen bond donor or acceptor function is selected from the group
consisting of ethyl acetate, acetone, acetonitrile, dimethylformamide, dimethylsulfoxide,
dioxane, ethanol, m-cresol, o-cresol, p-cresol, methanol, n-propanol, isopropanol,
n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl
ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl
methyl ether, anisole, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone
(MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone,
isophorone, isobutyraldehyde, furfural, methyl formate, methyl acetate, isopropyl
acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl
acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl
acetate, n-butyl propionate, n-pentyl propionate, triethylamine, 2-nitropropane, aniline,
N,N-dimethylaniline, nitromethane, tetrahydrofurane, and mixtures of two or more thereof.
8. The polymer composition according to any of the preceding claims, wherein the LDH
as defined in formula (1) has b + c in the range of 0 - 1.
9. The polymer composition according to any of the preceding claims, wherein the plasticizer
comprises at least one plasticizer selected from the group of phthalate, mellitate,
adipate, azelate, maleate, sebacate, epoxidized oil, chlorinated paraffin oil, polymeric
plasticizer or a mixture thereof.
10. The polymer composition according to any of the preceding claims, wherein the stabilizer
comprises at least one stabilizer selected from the group of lead-based stabilizer,
mixed metal-based stabilizer or a mixture thereof.
11. The polymer composition according to any of the preceding claims, wherein the LDH
further comprising a surface-treating agent, said surface-treating agent is an organic
moiety capable of covalent or ionic association with at least one surface of the layered
double hydroxide, and which modifies the surface properties of the layered double
hydroxide.
12. The polymer composition according to claim 11, wherein the surface-treating agent
is an organic moiety comprising at least 4 carbon atoms and at least one functional
group that is capable of covalent or ionic association with at least one surface of
the layered double hydroxide, said preferred surface-treating agent is selected from
organosilane compound, fatty acid or a salt thereof, a fatty acid/phosphoric acid
ester, polyhydric alcohol esters or a mixture thereof.
13. The polymer composition according to any of the preceding claims, wherein the polymer
composition is compounded by extrusion process at high temperature, preferably 150
- 190°C, more preferably 160-180°C and screw speed in the range of 30 - 100 rpm, preferably
40 -60 rpm.
14. An article comprising the polymer composition according to any of the preceding claims
, wherein the article is an electric or electronic circuit component, a structural
element for transportation and building or an indoor everyday object.
15. Electrical wire or cable coated with the polymer composition according to any of the
preceding claims.